Releasable coupling device for use with reinforcing tendons and method of using the same

ABSTRACT

A coupling device for attaching a protruding tendon disposed in a concrete structure to an extension strand comprises a barrel having a first end and a second end, a first conical bore disposed adjacent the first end having a first pair of wedges and sized to receive and grip the protruding tendon, a second conical bore disposed adjacent the second end and having a second pair of wedges and sized to receive and grip the extension strand, and a release bushing adapted for placement adjacent the first end of the barrel and having an aperture sized to receive the protruding tendon. The release bushing includes a contact surface positioned to contact the first pair of wedges and arranged to shift the first pair of wedges to a disengaged position in response to shifting the first end of the barrel toward the release bushing.

FIELD OF THE INVENTION

The present invention relates generally to reinforced concrete structures having reinforcing strands or tendons and, more specifically, to a coupling device for grasping a tendon protruding from a concrete structure.

BACKGROUND OF THE INVENTION

In many reinforced concrete structures one or more of the reinforcing strands or tendons may protrude from the structure. Typically, the protruding tendon is maintained at a desired tension by a pair of conical wedges that engage a conical bore in a wedge plate that bears against the concrete structure. For a variety of reasons, it may become necessary at some point to lessen the tension on the reinforcing tendon or to release the tendon entirely.

Unfortunately, in many applications, only a short piece of the tendon protrudes past the wedge plate. In such circumstances, there may not be enough of the tendon protruding beyond the wedge plate to permit the tendon to be suitably grasped by a tensioning ram. One approach for releasing the tension on such tendons is to cut away the original retaining wedges and/or a portion of the tendon, which permits the tension on the tendon to be released entirely. However, in some situations the tendon may be surrounded by grease, which may present a fire hazard when using a cutting torch. In still other situations, the use of cutting torches or other flames may not be advisable in any event due to other environmental concerns. Therefore, some provision for providing a coupling device for grasping and releasing the protruding strand and/or for permitting attachment to an extension strand may be desirable.

SUMMARY OF THE INVENTION

In one aspect of the invention, a coupling device for attaching a protruding tendon disposed in a concrete structure to an extension strand comprises a barrel having a first end and a second end, a first conical bore disposed adjacent the first end having a first pair of wedges, the first conical bore sized to receive the protruding tendon such that the protruding tendon is grippable by the first pair of wedges when the first pair of edges are shifted to an engaged position, a second conical bore disposed adjacent the second end and having a second pair of wedges, the second conical bore sized to receive the extension strand such that the extension strand is grippable by the second pair of wedges when the second pair of wedges are shifted to an engaged position, and a release bushing adapted for placement adjacent the first end of the barrel and having an aperture sized to receive the protruding tendon. The release bushing includes a contact surface positioned to contact the first pair of wedges and arranged to shift the first pair of wedges to a disengaged position in response to shifting the first end of the barrel toward the release bushing.

In further accordance with the disclosed example, the barrel may be separable into a first part and a second part, and the second part may include an internal spring positioned to bias the second pair of wedges in an outward direction. Each of the first part and the second parts may include a threaded internal bore, and a threaded barrel or plug may be used to join the first part to the second part. The internal spring may engage the threaded plug and the second pair of wedges. Preferably, the second pair of wedges are biased in an outward direction and are arranged to shift in an inward direction in response to insertion of the extension strand in the second conical bore.

The first conical bore and the first pair of wedges preferably are sized to expose a tip of the first pair of wedges. The first conical bore and the first pair of wedges may be sized to permit a tip of the first pair of wedges to extend out of the first conical bore when the first pair of wedges are in an engaged position. The release bushing may include an outer sidewall surrounding the contact surface, and the contact surface may be depressed relative to the outer sidewall. The outer sidewall includes an edge sized to engage a corresponding edge on the first end of the barrel when the release bushing is brought into contact with the barrel.

In accordance with another aspect of the invention, a coupling device for operatively connecting a protruding tendon disposed in a concrete structure to an extension strand includes a main body having a first end and a second end, a first bore disposed adjacent the first end and arranged to receive the protruding tendon, a first pair of wedges disposed within the main body adjacent the first end and shiftable between a disengaged position in which the protruding tendon is moveable within the first bore and an engaged position in which the protruding tendon is secured within the first bore, a second bore disposed adjacent the second end and arranged to receive the extension strand, a second pair of wedges disposed within the main body adjacent the second end and shiftable between a disengaged position in which the extension strand is moveable within the second bore and an engaged position in which the extension strand is secured within the second bore, and a release bushing. The release bushing may be adapted for placement adjacent the first end of the main body and preferably includes an aperture sized to receive the protruding tendon. The release bushing is positioned to contact the first pair of wedges and is arranged to shift the first pair of wedges to the disengaged position in response to shifting the main body toward the release bushing.

In accordance with a further aspect of the invention, a coupling device for operatively connecting a protruding tendon disposed in a concrete structure to an extension strand comprises a main body having a first end and a second end, first and second oppositely facing conical bores, the first bore arranged to receive the protruding tendon, a first pair of wedges disposed within the first bore and shiftable between a disengaged position in which the protruding tendon is axially moveable within the first bore and an engaged position in which the protruding tendon is secured within the first bore, a second pair of wedges disposed within the second bore and shiftable between a disengaged position in which the second pair of wedges are positioned to permit an extension strand to move axially within the second bore and an engaged position in which the second pair of wedges are positioned to grip an extension strand disposed within the second bore, and a release bushing. The release bushing is adapted for placement adjacent the first bore and includes an aperture sized to receive the protruding tendon, with the release bushing further including a first surface positioned to contact the first pair of wedges when the release bushing and the main body are brought toward each other to thereby shift the first pair of wedges to the disengaged position.

In a still further aspect of the invention, a method of changing the tension on a tendon protruding from a concrete structure comprises the steps of providing a chair sized to fit over a wedge plate, positioning the chair over the wedge plate, providing a coupling device having first and second pairs of oppositely facing wedges, securing the first pair of wedges to the protruding tendon, positioned an extension strand in the second pair of wedges, using a tensioning ram to grasp the extension strand and to apply a greater tension to the tendon to thereby displace the tendon away from a first position in a first direction, removing an original pair of wedges from adjacent the displaced tendon, and using the tensioning ram to displace the tendon in a second direction opposite the first direction to a second position.

In further accordance with a preferred form of the invention, the method may include the step of inserting a new pair of wedges adjacent the tendon when the tendon is adjacent the second position to maintain the tendon in the second position. The method also may include the step of placing a release bushing over the tendon prior to securing the first pair of wedges to the tendon, and may further include the step of displacing the tendon in the second direction until the release bushing forces the first pair of wedges to a disengaged position in which the tendon is released from the first pair of wedges.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective of a coupling device assembled in accordance with the teachings of the present invention;

FIG. 2 is an exploded view in perspective of the coupling device illustrated in FIG. 1;

FIG. 3 is a cross-sectional view of the coupling device and illustrating a reinforcing tendon and an extension strand both gripped by the coupling device;

FIG. 4 is a cross-sectional view similar to FIG. 3 and illustrating the reinforcing tendon in a de-stressed state having been released by the coupling device;

FIG. 5 is a fragmentary cross-sectional view illustrating an alternate embodiment of the coupling device and showing the reinforcing tendon and the extension strand both gripped by the coupling device;

FIG. 6 is a cross-sectional view similar to FIG. 5 and illustrating the reinforcing tendon in a de-stressed state having been released by the coupling device;

FIG. 7 is a fragmentary cross-sectional view of a concrete reinforced structure having a tendon protruding from a wedge plate and showing a de-tensioning chair in place over the wedge plate;

FIG. 8 is a fragmentary cross sectional view similar to FIG. 7 and illustrating one end of the coupling device attached to the protruding portion of the tendon and illustrating an extension strand protruding from another end of the coupling device;

FIG. 9 is a cross-sectional view similar to FIG. 8 and showing the tendon displace to the right of the Figure by the tensioning ram thereby permitting the original wedges to be removed from the wedge plate;

FIG. 10 is a cross-sectional view similar to FIG. 9 and illustrating the existing strand being displaced to the left of the Figure by the tensioning ram; and

FIG. 11 is a cross-sectional view similar to FIG. 10 and illustrating the release bushing in contact with the wedge plate and shifting the internal wedges to a release position thereby releasing all tension on the tendon.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The examples described herein are not intended to be exhaustive or to limit the scope of the invention to the precise form or forms disclosed. Rather, the following exemplary embodiments have been chosen and described in order to best explain the principles of the invention and to enable others skilled in the art to follow the teachings thereof.

Referring now to FIGS. 1-4 of the drawings, a coupling device assembled in accordance with the teachings of a first disclosed example of the present invention is shown and is generally referred to the reference numeral 20. As shown in FIGS. 7 through 11, the coupling device 20 is generally intended for use with a tendon 22 that protrudes from a concrete structure 24. As is generally known, the tendon 22 includes an original pair of wedges 26 a and 26 b, which are disposed in a generally conical bore 28 of a wedge plate 30. The tendon 22 includes an end 22 a. Also, it will be appreciated that the concrete structure 24 may include a number of protruding tendons 22.

The coupling device 20 includes a barrel 32 having a first end 34 and a second end 36. A first conical bore 38 is formed in the barrel 32 generally adjacent to the first end 34, and a second conical bore 40 is formed in the barrel 32 generally adjacent to the second end 36. As will be discussed in greater detail below, the first conical bore 38 is size to receive at least a portion of the protruding tendon 22. A first pair of wedges 42 are disposed in the first conical bore 38, with the first pair of wedges 42 being arranged to grip the tendon 22 when the tendon 22 is disposed within the first conical bore 38. A second pair of wedges 44 are disposed within the second conical bore 40, with the second pair of wedges 44 being arranged to grip an extension strand 46 as will be explained in greater detail below. The construction of the first and second pairs of wedges 42 and 44 may be conventional and would be known to those of ordinary skill in the art.

As shown in FIGS. 1 and 4, a release bushing 48 may be provided. The release bushing 48 preferably includes an aperture 50 which is sized to fit over the tendon 22. In the disclosed example, the aperture 50 comprises a generally round hole through the release bushing 48. Alternatively, the aperture 50 may comprise a slot in the release bushing 48. The release bushing 48 includes a first end 52 which is generally sized and positioned to make contact with a surface, such as a surface 52 on the wedge plate 30. The release bushing 48 also includes a second end 56. The release bushing 48 also includes a contact surface 58. In the disclosed example, the contact surface 58 is defined by a depressed center 60 formed in the release bushing 48. The depressed center 60 may generally surround the aperture 50. Alternatively, and as discussed in greater detail below and as is shown in FIGS. 5 and 6, the contact surface 58 may be formed by the second end 56. In the disclosed example of FIGS. 1 through 4, the release bushing 48 includes a raised sidewall or skirt 62, with the skirt 62 generally surrounding the aperture 50. The skirt 62 includes an edge 64.

As shown in FIG. 2, the coupling device 20 may be separable into a first half 66 and a second half 68. Referring to FIGS. 2-4, the first-half 66 may be positioned generally toward the concrete structure 24, while the second-half 68 may be positioned generally away from the concrete structure 24. Also, it will be appreciated that the first conical bore 38 is formed in the first half 66, while the second conical bore 40 is formed in the second half 68. The first half 66 preferably includes a threaded portion 70, while the second half 68 preferably includes a threaded portion 72. A threaded barrel or plug 74 may be provided in order to permit the first half 66 to be joined to the second half 68.

It will be appreciated that, in the disclosed example, the first conical bore 38 and the second conical bore 40 are axially aligned with each other. Also, the first threaded portion 70 and the second threaded portion 72 of the first and second halves 66 and 68, respectively, are generally axially aligned with each other. A spring 76 may be provided, with the spring 76 bearing against the plug 74 and the second pair of wedges 44. Accordingly, the second pair of wedges 44 will be biased outwardly and away from the structure 24 when viewing FIGS. 3 & 4. As an alternative, the first half 66 and the second half to 68 may be joined together using any other suitable method of connection. As a still further alternative, the first half 66 and the second half 68 may be integrally formed into a single main body. Also, the spring 76 may bear against some other ledge or abutment (not shown) as may suitably be provided by those of skill in the art.

The first pair of wedges 42 are shiftable between a retracted or disengaged position and an extended or engaged position. When the first pair of wedges 42 are disposed in the disengaged position, it will be appreciated that the wedges 42 have generally been shifted into or toward a widened portion 38 a of the first conical bore 38. On the other hand, when the first pair of wedges 42 are disposed in the engaged position, it will be appreciated that the first pair of wedges 42 have generally been shifted into or toward a narrowed portion 38 b of the first conical bore 38.

Similarly, when the second pair of wedges 44 are disposed in the disengaged position, it will be appreciated that the second pair of wedges 44 have generally been shifted into or toward a widened portion 40 a of the second conical bore 40. On the other hand, when the second pair of wedges 44 are disposed in the engaged position, it will be appreciated that the second pair of wedges 44 have generally been shifted into or toward a narrowed portion 40 b of the second conical bore 40.

As would be known to those of skill in the art, when either the first pair of wedges 42 or the second pair of wedges 44 are disposed toward their respective engaged positions, the wedges will grasp or otherwise secure a cable, tendon, or strand disposed in the appropriate conical bore. Accordingly, it will be appreciated that, when the tendon 22 is disposed in the first conical bore 38 and the first pair of wedges and 42 are in the disengaged position disposed toward the widened the portion 38 b , that the tendon and 22 may be shifted axially within the first conical bore 38. However, when tension is applied to the tendon 22 (i.e., either the tendon 22 is pulled in one direction or the coupling device 20 is pulled in the opposite direction), the tendon 22 will, due to frictional forces, be gripped by the first pair of wedges 42 as the first pair of wedges 42 are shifted toward the narrowed portion 38 b of the bore 38. Thus, the first pair of wedges 42 will apply a progressively greater gripping force to the tendon 22.

Similarly, when the extension strand 46 is disposed in the second conical bore 40 and the second pair of wedges 44 are in the disengaged position disposed toward the widened portion 40 a, the extension strand 46 may be shifted axially within the second conical bore 40. However, when tension is applied to the extension strand 46, the extension strand 46 will, due to the frictional forces, be gripped by the second pair of wedges 44 as the second pair of wedges 44 are shifted toward the narrowed portion 40 b of the second conical bore 40. Thus, the second pair of wedges 44 will apply a progressively greater gripping force to the extension strand 46.

Referring now to FIG. 3, it will be appreciated that the extension strand 46 may be inserted into the coupling device 20 when the coupling device 20 is fully assembled with the first and second halves 66 and 68 joined together by the plug 74. The second pair of wedges 44 are, by virtue of the spring 76, normally disposed in the engaged position in which the second pair of wedges 44 are biased outwardly and toward the right of the Figure toward the engaged position under the force of the spring 76. Upon inserting an end 46 of the extension strand 46 into the second conical bore 40, the insertion force of the extension strand 46 will shift the second pair of wedges 44 toward the widened portion 40 b of the bore 40, until the second pair of wedges have spread apart enough such that the and 46 a of the extension strand 46 will fit between the second pair of wedges 44. At this point, tension applied to the extension strand 46 will, due to frictional forces, cause the second pair of wedges 44 to apply a progressively greater gripping force to the extension strand 46 in a known manner.

Referring now to FIGS. 3, 4 and 8, it will be appreciated that, in the disclosed example, the first pair of wedges 42 and/or the first conical bore 38 may be sized and/or shaped using known principles such that an end or tip 80 of the first pair of wedges 42 will be exposed or otherwise protrude from the narrowed portion 38 b of the first conical bore 38.

As an alternative, and referring to FIGS. 5 and 6, the first end 34 of the coupling device 20 may include a countersunk bore 82 that connects with the first conical bore 38. Should the coupling device 20 be structured as shown in FIGS. 5 and 6, then a modified release bushing 49 may be constructed as is shown in FIGS. 5 and 6. Using the modified form of the release bushing 49, it will be appreciated that the release bushing 49 and/or the countersunk bore 82 are sized such that the release bushing 49 will fit into the countersunk bore 82 so as to come into contact with the exposed tip 80 of the first pair of wedges 42 as will be discussed in greater detail below. In the construction of FIGS. 5 and 6, a first end 84 of the bushing 49 is generally flat and generally similar to the first end 52 of the release bushing 48, while a second end 86 of the bushing 89 is generally flat and forms a contact surface 88. The contact surface 88 will form the surface that makes contact with the tip 80 of the first pair of wedges 42 as will be discussed in greater detail below.

Referring now to FIGS. 7 through 11, a chair 90 is preferably provided. The chair 90 facilitates the use of a conventional tensioning ram 92 (shown schematically in FIGS. 8 through 11). The details of a suitable chair 90 and the operation of the tensioning ram 92 is known to those of skill in the art. As would be known, the chair 90 is sized to fit over the wedge plate 30 so as to bear against a surface 24 a of the concrete structure 24. Preferably, the chair 90 includes a surface 91 and one or more legs 94 which are sized and positioned to make contact with the surface 24 a of the concrete structure 24, with the legs 94 preferably sized to defined a working area 96.

In operation, the coupling device 20 assembled in accordance with the teachings of either disclosed embodiment of the present invention may be used in at least two exemplary operational modes. For example, in certain circumstances a user (not shown) may desire to lessen the tensile force on one or more all of the tendons 22. In such a situation, the coupling device 20 disassembled in accordance with the foregoing discussion with the first and second sets of wedges 40, 42 disposed in their respective conical boars 38, 40. The coupling device 20 is positioned over the protruding tendon 22 and attached to and end 22 a of the tendon 22 in a known manner. This step may require that the coupling device 20 be separated into its first and second halves 66, 68, which is accomplished by unthreading at least the first half 66 from the plug 74. The first pair of wedges 42 also are inserted into the first conical bore 38 in a known manner, and the coupling device 20 may be fully re-assembled.

By applying a pulling force to the coupling device 20, the first pair of wedges 42 will suitably grip the tendon 22. The end 46 a of the extension strand 46 is inserted into the second conical bore as discussed above, such that the second pair of wedges 44 will be positioned to apply a gripping force to the extension strand 46. The user then attaches the conventional tensioning ram 92 to the extension strand 46 and prepares to apply a pulling or tensile force to the extension strand 46 in a known manner. The step may require the tensioning ram 92 to bear against the concrete structure 24 and/or the chair 90.

Upon applying a pulling or tensile force to the extension strand 46, the coupling device 20 transfers the force from the extension strand 46 to the tendon 22. In the process, as the extension strand 46 and the coupling device 20 are suitably displaced to the right when viewing the FIGS., the tendon 22 is also suitably displaced in the same direction. When this displacement occurs, the user may remove the original pair of wedges 26.

At this point, the tensioning ram 92 may be tensioned in a controlled manner as would be known, thereby permitting the coupling device 20 to be displaced back toward the concrete structure 24 and past the original position of the coupling device 20. As the coupling device 20 passes its original position and is now disposed closer toward the concrete structure 24, it will be appreciated that the tension on the tendon and 22 is now reduced relative to the original tension. When a desired position and/or tension is achieved, a user may simply insert a replacement pair of wedges 100 into the conical bore 28 in the wedge plate 30. The tendon 22 is now suitably de-tensioned.

In a preferred mode of operation of the present invention, the coupling device 20 may be used to completely release the tendon 22 as is shown in FIGS. 7 through 11. The coupling device 20 is secured to the protruding tendon 22 in the manner outlined above, and the tensioning ram 92 is secured to the extension strand 46 in the manner outlined above. Preferably, the release bushing 48 is first positioned over the protruding tendon 22. Alternatively, should the bushing 48 be provided with a slot as opposed to a round aperture 50, then the release bushing 48 may be suitably positioned adjacent to the tendon 22 later in the process. Using the tensioning ram 92, again the extension strand 46 and the coupling device 20 are suitably displaced away from the concrete structure 24 until the user can remove the original pair of wedges 26. At this point, the tensioning ram 92 is suitably de-tensioned, allowing the coupling device to be displaced back toward the concrete structure 24.

When the coupling and device 20 is shifted far enough back toward the concrete structure 24, the exposed tip 80 of the first pair of wedges 42 will make contact with the contact surface 58 on the release bushing 48. When this contact is made, no further movement of the wedges toward the concrete structure 24 is possible. However, due to continued the de-tensioning, the coupling device 20 will continue moving toward the concrete structure 24. This relative movement between the coupling device and the now-stationary first pair of wedges 42 causes the first pair of wedges 42 to shift gradually into the widened portion 38 a of the first conical bore 38, which eventually causes the first pair of wedges 42 release their frictional grip on the tendon 22. At this point, the tendon 22 is completely released and may slide or otherwise displace completely into the concrete structure 24.

In accordance with the disclosed example, the coupling device 20 of the present invention may permit the tension on the tendon 22 to be released entirely without having to resort to the use of cutting devices, torches, or other methods of release involving flames and/or heat. Thus, in those circumstances or environments where the use of torches, etc., is not advisable, the coupling device 20 of the present invention offers, in accordance with the disclosed example, certain advantages that are not achievable using standard prior art coupling devices.

Numerous additional modifications and alternative embodiments of the invention will be apparent to those skilled in the art in view of the foregoing description. This description is to be construed as illustrative only, and is for the purpose of teaching those skilled in the art the best mode of carrying out the invention. The details of the structure and method may be varied substantially without departing from the spirit of the invention, and the exclusive use of all modifications which come within the scope of the appended claims is reserved. 

1. A coupling device for attaching a protruding tendon disposed in a concrete structure to an extension strand, the coupling device comprising: a barrel having a first end and a second end; a first conical bore disposed adjacent the first end having a first pair of wedges, the first conical bore sized to receive the protruding tendon such that the protruding tendon is grippable by the first pair of wedges when the first pair of edges are shifted to an engaged position; a second conical bore disposed adjacent the second end and having a second pair of wedges, the second conical bore sized to receive the extension strand such that the extension strand is grippable by the second pair of wedges when the second pair of wedges are shifted to an engaged position; and a release bushing, the release bushing adapted for placement adjacent the first end of the barrel and having an aperture sized to receive the protruding tendon, the release bushing including a contact surface positioned to contact the first pair of wedges, the contact surface of the release bushing arranged to shift the first pair of wedges to a disengaged position in response to shifting the first end of the barrel toward the release bushing.
 2. The coupling device of claim 1, wherein the barrel is separable into a first part and a second part, and wherein the second part includes an internal spring positioned to bias the second pair of wedges in an outward direction.
 3. The coupling device of claim 2, wherein each of the first part and the second part includes a threaded internal bore, and including a threaded barrel for joining the first part to the second part.
 4. The coupling device of claim 3, wherein the internal spring engages the threaded barrel and the second pair of wedges.
 5. The coupling device of claim 1, wherein the second pair of wedges are spring biased in an outward direction, and further wherein the second pair of wedges are arranged to shift in an inward direction in response to insertion of the extension strand in the second conical bore.
 6. The coupling device of claim 1, wherein the first conical bore and the first pair of wedges are sized to expose a tip of the first pair of wedges.
 7. The coupling device of claim 1, wherein the first conical bore and the first pair of wedges are sized to permit a tip of the first pair of wedges to extend out of the first conical bore when the first pair of wedges are in an engaged position.
 8. The coupling device of claim 7, wherein the release bushing includes an outer sidewall surrounding the contact surface, the contact surface depressed relative to the outer sidewall.
 9. The coupling device of claim 8, wherein the outer sidewall includes an edge sized to engage a corresponding edge on the first end of the barrel when the release bushing is brought into contact with the barrel.
 10. A coupling device for operatively connecting a protruding tendon disposed in a concrete structure to an extension strand, the coupling device comprising: a main body having a first end and a second end; a first bore disposed adjacent the first end and arranged to receive the protruding tendon; a first pair of wedges disposed within the main body adjacent the first end, the first pair of wedges shiftable between a disengaged position in which the protruding tendon is moveable within the first bore and an engaged position in which the protruding tendon is secured within the first bore; a second bore disposed adjacent the second end and arranged to receive the extension strand; a second pair of wedges disposed within the main body adjacent the second end, the second pair of wedges shiftable between a disengaged position in which the extension strand is moveable within the second bore and an engaged position in which the extension strand is secured within the second bore; and a release bushing, the release bushing adapted for placement adjacent the first end of the main body and having an aperture sized to receive the protruding tendon, the release bushing positioned to contact the first pair of wedges, the release bushing arranged to shift the first pair of wedges to the disengaged position in response to shifting the main body toward the release bushing.
 11. The coupling device of claim 10, wherein the first bore is aligned with the second bore.
 12. The coupling device of claim 10, wherein the second pair of wedges are biased toward the engaged position, the second pair of wedges arranged to shift toward the disengaged position in response to inserting the extension strand into the second bore.
 13. The coupling device of claim 12, wherein the main body is separable into a first part and a second part, and wherein the second part including the second bore, the second part further including an internal spring positioned to bias the second pair of wedges toward the engaged position, the spring bearing against a plug threaded into the first bore and the second bore.
 14. The coupling device of claim 10, wherein the first pair of wedges include a tip, the first bore and the first pair of wedges sized to expose the tip when the first pair of wedges are in the engaged position.
 15. The coupling device of claim 10, wherein the first bore and the first pair of wedges are sized to position the first pair of wedges for contact with the release bushing when the first pair of wedges are in the engaged position.
 16. The coupling device of claim 15, wherein the first bore is conical, the first pair of wedges sized to protrude from the first bore when the first pair of wedges are in the engaged position, and wherein the release bushing includes an outer sidewall surrounding a depressed contact surface.
 17. The coupling device of claim 16, wherein the outer sidewall defines a contact surface positioned to engage a first end of the body when the release bushing is brought into contact with the body.
 18. A coupling device for operatively connecting a protruding tendon disposed in a concrete structure to an extension strand, the coupling device comprising: a main body having a first end and a second end; first and second oppositely facing conical bores, the first bore arranged to receive the protruding tendon; a first pair of wedges disposed within the first bore and shiftable between a disengaged position in which the protruding tendon is axially moveable within the first bore and an engaged position in which the protruding tendon is secured within the first bore; a second pair of wedges disposed within the second bore and shiftable between a disengaged position in which the second pair of wedges are positioned to permit an extension strand to move axially within the second bore and an engaged position in which the second pair of wedges are positioned to grip an extension strand disposed within the second bore; and a release bushing, the release bushing adapted for placement adjacent the first bore and having an aperture sized to receive the protruding tendon, the release bushing including a first surface positioned to contact the first pair of wedges when the release bushing and the main body are brought toward each other to thereby shift the first pair of wedges to the disengaged position.
 19. The coupling device of claim 18, wherein the first bore is axially aligned with the second bore, and including a spring disposed adjacent the second pair of wedges and arranged to bias the second pair of wedges toward the engaged position, the spring arranged to permit the second pair of wedges to shift toward the disengaged position in response to insertion of the extension strand into the second bore.
 20. The coupling device of claim 19, wherein the main body includes a first part and a second part joined by a threaded plug, the spring positioned to bear against the threaded plug.
 21. The coupling device of claim 20, wherein the first pair of wedges include a tip sized to protrude from the first bore when the first pair of wedges are in the engaged position, and wherein the first surface of the release bushing is defined by a depressed central portion surrounding the aperture.
 22. The coupling device of claim 21, wherein the release bushing includes an outer sidewall surrounding the depressed central portion.
 23. A method of releasing the tension on a tendon protruding from a concrete structure comprising the steps of: providing a chair sized to fit over a wedge plate; positioning the chair over the wedge plate; providing a coupling device having first and second pairs of oppositely facing wedges; providing a release bushing over the protruding tendon and positioned to engage the first pair of wedges; securing the first pair of wedges to the protruding tendon; positioned an extension strand in the second pair of wedges; using a tensioning ram to grasp the extension strand and to apply a greater tension to the tendon to thereby displace the tendon away from a first position in a first direction; removing an original pair of wedges from adjacent the displaced tendon; using the tensioning ram to displace the tendon in a second direction opposite the first direction to a second position; and displacing the tendon in the second direction a distance sufficient to cause the release bushing to shift the first pair of wedges out of engagement with the protruding tendon. 